1. Academic Department of Trauma and Orthopaedics, School of Medicine, University of Leeds, Clarendon Wing, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK.
2. Department of Trauma and Orthopaedics, Leeds Teaching Hospitals NHS Trust, Beckett Street, Leeds LS9 7TF, UK.
3. Massachusetts General Hospital, 55 Fruit Street, Boston, Massachusetts 02114, USA.